Abstract

Loss of endothelial barrier integrity is of key importance in a number of neuropathological conditions. Blood-Brain barrier (BBB) disruption, in part driven by cytokines, is an early event in the pathogenesis of Multiple Sclerosis(MS), an inflammatory autoimmune disorder caused by the presence of multifocal demyelinating lesions within the CNS. Astrocyte-derived sonic hedgehog (Shh) promotes BBB formation and a reduction in Shh levels has been reported in MS patients. Low circulating levels of Vitamin D3 are associated with an increased risk of MS although the molecular pathways underlying Vitamin D3 effects on MS pathogenesis remain elusive. Interplay between Shh and Vitamin D3 pathways has been reported in other cell types but this has not been yet studied in the context of the BBB. Several microRNAs are regulated in MS but their function is not always clear.The hypothesis that under inflammatory conditions, Shh and Vitamin D3 signalling pathways may interact in order to promote endothelial barrier stability and/or prevent cytokine-driven BBB disruption was tested. A murine and a human endothelial barrier model were established and explored in the context of inflammation. Shh and Vitamin D3 treatment prevented cytokineinduced endothelial barrier disruption, in both model systems, possibly through the regulation of metalloproteinase expression and/or localisation. In addition, analysis of the human endothelial BBB barrier model suggested that miR125b is a possible candidate to exacerbate cytokine-driven loss in barrier integrity.Analysis of microarray data with the human BBB model revealed that Shh andVitamin D3 treatment could prevent cytokine-driven tissue factor (TF/F3) expression, suggesting that this could be an additional mechanism by which Shh and Vitamin D3 can mediate their protective synergy against cytokinedriven barrier dysfunction.Overall the data suggests that cross-talk between Shh and Vitamin D3 may provide a new approach to reducing loss off BBB integrity.